Waterless printing (sometimes known as driography) is a method of printing that provides high quality reproduction without recourse to a dampening system, or fountain solution, on the printing press. Without the problem of water-induced ink emulsification, prints exhibit sharper dots and good tonal gradation with little variation in density throughout the printing run. These improvements are accomplished without sacrificing printing speed or cost.
The main advantage of a waterless system is that imaging only requires exposure and not a subsequent wet development step. This allows an exposure system to be included in the press itself, so that plates can be mounted, exposed and inked directly without the need to remove the exposed plates for development.
Printing plates can be exposed by various kinds of radiation, in an analog or digital fashion, including thermal and laser radiation. (See generally Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 19, 1982, pages 110-163). The use of lasers to expose printing plates is known to those skilled in the art, and it is preferred that the inventive plates described hereinafter be exposed by laser radiation.
Many modifications to printing plates for use in waterless printing have been proposed in the past but all require wet development. Recent work on waterless, or dry, plates, which require no dampening solutions, has employed organopolysiloxane as an ink-repelling layer which is adhered to a photosensitive layer containing a quinone diazide (see C. Ichijo and M. Asano, Japanese Patent Application No. 62-161154, Jul. 17, 1987). Other work by N. Kawabe, et al., Japanese Patent Publication No. 2-61730, Dec. 20, 1990, describes a photosensitive resin layer without pigments or dyes, which absorbs UV light, and a top layer made of silicone rubber. However, after analog exposure, this printing plate is wet developed.
T. Taguchi and K. Ueyama disclose in Japanese Patent Application No. 63-22687, Jan. 30, 1988, a multilayer waterless plate having a non-uniform fluorinated layer on top. This fluorinated material, is in the form of a dispersion, rather than in solution as described in the present invention. Also, the image is made with a hot nib thermal line printer, which does not involve removing any material from the surface during exposure.
European Patent 0 306 932 B1 (Jun. 29, 1994) discloses a single layer printing plate containing polytetrafluoroethylene. This plate is used for relief printing, and after photopolymerization, the remaining non-polymerized material, which is soluble, is removed.
Clearly, waterless printing plates and a method of developing said plates, which overcome some of the problems and deficiencies of the prior art, are needed. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the drawings and detailed description which hereinafter follows.